Add station dashboard with auth and historical data recording

- Protected /dashboard route with PBKDF2 password + HMAC-signed cookies
- First-run setup flow at /dashboard/setup
- Records Ambient station readings to daily JSONL files in app/data/station/
- Deduplicates on dateutc so 1-min polling never writes duplicate rows
- Dashboard charts: temp, humidity/dew, wind+gusts, wind rose, pressure,
  rain rate, rain accumulation, UV, solar radiation
- History range selector: 1h / 6h / 24h / 7d / 30d / 90d / 1y / 2y / 3y
- Auto-downsamples to 720 points for long ranges
- Cron interval changed from 10 min to 1 min (with dedup guard)
- app/data/ added to .gitignore (contains keys and session secret)

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.gitignore

@@ -1,2 +1,3 @@
 app/node_modules/
+app/data/
 .env